Valve has released SteamPlay Beta for Linux. It includes a modified distribution of Wine, to provide compatibility with Windows game titles. The included improvements to Wine have been designed and funded by Valve, in a joint development effort with CodeWeavers.

Here are some examples of what they been working on together since 2016:

Proton, the tool that Steam Play uses to provide Windows compatibility, contains a custom version of Wine as well as additional libraries developed alongside it. It's fully open-source and available on GitHub.